Ink-jet printers offer a low cost, high quality, and comparatively noise-free option to other types of printers commonly used with computers. Such printers employ a resistor element in a chamber provided with an egress for ink to enter from a plenum. The plenum is connected to a reservoir for storing the ink. A plurality of such resistor elements are arranged in a particular pattern, called a primitive, in a printhead. Each resistor element is associated with a nozzle in a nozzle plate, through which ink is expelled toward a print medium. The entire assembly of printhead and reservoir comprise an ink-jet pen.
On operation, each resistor element is connected via a conductive trace to a microprocessor, where current-carrying signals cause one or more selected elements to heat up. The heating creates a bubble of ink in the chamber, which is expelled through the nozzle toward the print medium. In this way, firing of a plurality of such resistor elements in a particular order in a given primitive forms alphanumeric characters, performs area-fill, and provides other print capabilities on the medium.
Ink-jet inks used in thermal ink-jet printing typically comprise a colorant and a vehicle, with the vehicle often containing water and other relatively low surface tension liquids.
There are two general classifications of colorants: dye-based and pigment-based. Dyes have the advantage of being water-soluble. However, problems with dyes include poor waterfastness, poor smearfastness, poor bleed control between colors, and poor lightfastness. Pigments are generally not soluble in water and require a dispersant or other means to make it soluble in water.
Although the relevant art contains many examples of ink-jet ink formulations using these colorants, a need still exists for ink compositions comprising stable, water soluble pigments which provide improved smearfastness, waterfastness, improved print quality, improved bleed control, and optical density.